US4151490A - Automatic cable equalizer circuit - Google Patents

Automatic cable equalizer circuit Download PDF

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Publication number
US4151490A
US4151490A US05/811,291 US81129177A US4151490A US 4151490 A US4151490 A US 4151490A US 81129177 A US81129177 A US 81129177A US 4151490 A US4151490 A US 4151490A
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United States
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signal
cable
signals
output
amplitude
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Expired - Lifetime
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US05/811,291
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English (en)
Inventor
Lucas J. Bazin
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RCA Corp
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RCA Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/04—Control of transmission; Equalising
    • H04B3/14—Control of transmission; Equalising characterised by the equalising network used
    • H04B3/143—Control of transmission; Equalising characterised by the equalising network used using amplitude-frequency equalisers
    • H04B3/145—Control of transmission; Equalising characterised by the equalising network used using amplitude-frequency equalisers variable equalisers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/10—Adaptations for transmission by electrical cable
    • H04N7/102—Circuits therefor, e.g. noise reducers, equalisers, amplifiers

Definitions

  • This invention relates to cable equalizer circuits for compensating signals being transmitted over a cable for cable attenuation losses, and in particular to an automatic cable equilizer for compensating video signals from a television camera.
  • Cable losses may be generally categorized as resistive losses and capacitive or dielectric losses. The first of these, attributed to the resistance value of the cable, causes a relatively linear attenuation over the frequency range of the signal being transmitted and is generally not of significant concern. However, cable losses, attributed to the capacitance of the cable, is of major concern as its affect is to attenuate the higher frequencies of the signal being transmitted.
  • the problem of cable attenuation of the signal is further increased where the length of the cable is varied as often occurs when switching between video sources located at varying distances from the main video processing apparatus. Since a fixed cable compensation will not satisfy the typical video cable installation, it is common practice to view the signal being received on a waveform monitor and manually switch in cable compensation circuits, which, for example, may be in the form of high frequency emphasis networks to compensate for the high frequency losses occurring in the cable.
  • a signal cable equalizer circuit for automatically compensating signals transmitted over a cable, wherein the cable signals incur amplitude and frequency response losses during the transmission.
  • the circuit comprises means for including a reference signal having both low and high frequency components in the signal to be transmitted, the reference signal components exhibiting a relative difference in amplitude as a result of transmission losses.
  • Signal summing means are responsive to the cable signals for providing an output signal.
  • Signal processing means are coupled to the cable signals for developing a correction signal derived from the cable signal.
  • Detector means are coupled to the signal summing means for developing a control signal proportional to the relative amplitude difference between the low and high frequency reference signal components.
  • Multiplier means are responsive to the correction signal and the control signal for coupling an amount of the correction signal as determined by the control signal to the signal summing means for restoring the amplitude of the output signal.
  • FIG. 1 is a block diagram of an automatic cable equalizer circuit embodying the present invention.
  • FIGS. 2a & 2b illustrate waveforms useful in understanding the operation of the apparatus shown in FIG. 1.
  • a video signal (Video In) from, for example, a television camera, is coupled to the sending end of a cable 10.
  • cable 10 is shown of indeterminent length in the Figure, typical installations may include cable lengths which vary from a few feet up to 1,000 feet or more.
  • the signal at the output of cable 10 is coupled to the input terminals of an amplifier 12.
  • Amplifier 12 is of the type known as a differential amplifier which is particularly advantageous for its ability to reject common mode signals, such as noise induced in the cable, and for its ability to develop two identical output signals, the first of which is coupled by means of resistor 14 to the input of signal summing output amplifier comprising amplifier 18, input resistors 14, 20 and feedback resistor 16.
  • the output terminal of the signal output amplifier provides a convenient terminal (Video Out) from which the video signal from the cable may be coupled to further video processing equipment, not shown.
  • the other output signal from input amplifier 12 is coupled to a high frequency emphasis network 26 and to a sync and burst separator and burst gate generator 28.
  • High frequency emphasis network 26 develops a signal output which is complementary to the signal applied to its input terminal, that is, its amplitude versus frequency response transfer characteristic rises as the frequency of the input signal increases, thereby providing an output signal which increases in amplitude as the frequency of the input signal rises.
  • the characteristics of network 26 are selected so as to provide an amplitude increase which is opposite and equal or complementary to the attenuation the video signal incurs during its transmission over cable 10.
  • the output signal from network 26 is coupled to one input (X) of a multiplier 24 (constructed, for example, from a Motorola MC-1595 integrated circuit).
  • the output of the multiplier 24 is coupled to a second input of the signal summing output amplifier 18 by means of resistor 20.
  • a control signal generated in accordance with the invention, and to be described below, is coupled to the other input (Y) of multiplier 24 to determine the proportion of the above-described complementary correction signal to be added to the attenuated input signal at the input of the video signal output amplifier.
  • the attenuated video signal from cable 10 is coupled directly to the signal output amplifier where it has added to it a correction signal equal and opposite to the signal attenuation incurred in transmission over cable 10 so as to provide at the Video Out terminal a video signal in which the amplitude of the output signal is equal to the original signal applied to the input end of cable 10.
  • the control signal for the (Y) input of multiplier 24 is generated as follows.
  • a reference signal is inserted in the signal to be transmitted over the cable to serve as an index of the loss incurred during transmission.
  • the signal being transmitted is a television video signal
  • this may be conveniently accomplished by including the reference signal in the horizontal blanking interval, although it is feasible to place the reference signal at any desired position in the signal to be transmitted. Since the reference is included in the signal to be transmitted, it is necessary that the reference signal be in a form that will indicate on its arrival at the receiving end of the cable the overall signal attenuation that has occurred, as well as the change in attenuation over the frequency range of the signal due to the varying cable lengths.
  • the reference signal to be included contains both a low frequency and high frequency component so as to effectively indicate at the receiving end of cable 10, the relative attenuation over the frequency range of the transmitted signal. If the signal being transmitted is in the form of a composite video signal containing both synchronizing and color burst components, then these signal components, which normally occur during the blanking interval and are at 15,750 Hz and 3.58 MHz, respectively, (U.S. standards) may be advantageously utilized as the reference signal. If the signal being transmitted does not include the horizontal synchronizing and burst signal components, then suitable signal components of similar frequency identity may be inserted to serve as the reference signal.
  • FIG. 2a illustrates a typical horizontal blanking interval with a horizontal synchronizing component of amplitude "a" occurring at time t 1 -t 2 and a color burst signal of amplitude "b" occurring at time t 3 -t 4 .
  • the waveform of FIG. 2a when applied to the input end of cable 10 is attenuated in its transmission so as to appear at the receiving end of the cable 10 in the form illustrated in FIG. 2b.
  • FIG. 2a illustrates a typical horizontal blanking interval with a horizontal synchronizing component of amplitude "a" occurring at time t 1 -t 2 and a color burst signal of amplitude "b" occurring at time t 3 -t 4 .
  • the low frequency component occurring during time t 1 -t 2 is shown as of only slightly reduced amplitude "a'” due to resistive losses with a rounded leading edge due to dielectric losses based on the length of the cable; the high frequency component occurring during the time t 3 -t 4 is shown of significantly reduced amplitude "b'" which is due virtually entirely to the dielectric losses in the cable and is proportional to the length of the cable.
  • the present invention makes use of the difference or ratio of amplitudes between the low frequency and high frequency components of the reference signal to establish the extent of the cable attenuation due to the attenuation of the high frequency component relative to the low frequency component.
  • This attenuation ratio is a virtual measure of the length of cable over which the signal is being transmitted.
  • the attenuated incoming video signal is applied to the input terminal of sync and burst separator and burst gate generator 28 which separates the horizontal synchronizing component and burst component in a manner well known to those skilled in the art, so as to provide a reference signal gating signal indicating the time occurrence of the reference signals.
  • the output gating signals of separator 28 are coupled to an input of gated detector 30 and to a gated feedback clamp 22 coupled to the signal output amplifier to insure sampling of the attenuated reference signal components only during the desired period of the blanking interval.
  • the other input of gated detector 30 is coupled to the video output terminal.
  • the attenuated video signal in the main video path Video-In to Video-Out terminals is coupled to two peak detectors, one for sync and one for burst, in gated detector 30.
  • Reference signal gating signals from separator 28 gate the respective peak detectors to provide a D.C. level at the output of gated detector 30, which represents the amplitude difference of sync and burst levels at the output video terminal.
  • the output of detector 30 is coupled to the input terminal of an amplifier 32, filter 36 and, in turn, to multiplier control input (Y).
  • Y multiplier control input
  • the high frequency (burst) component of the reference decreases in amplitude relative to the low frequency (sync) component of the reference; this relative amplitude difference results in a D.C. output level from gated detector 30 reflecting the amplitude difference due to attenuation of the reference signals being transmitted over the cable. Therefore, the D.C. output of detector 30, which changes with cable length, is updated once each television line and automatically adjusts the control voltage at the (Y) input of multiplier 24 to add a correction signal in the form of a complementary signal, so as to restore the low (sync) and high (burst) reference signals to their original values at the input end of cable 10.
  • Network 26 is typically designed for the largest expected cable length, i.e., 1000', and multiplier 24 thus automatically provides the proper amount of correction for values of cable length from 0 to 1000'.
  • the relatively large amount of cable attenuation compensation required to be provided by high frequency emphasis network 26 may be further linearized in the mid-range values by additional feedback in the form of resistive or a combination of reactive and resistive feedback, as illustrated by linearity network 34 coupled from the output terminal of the signal output amplifier to the input terminal of the traditional high frequency emphasis circuitry.
US05/811,291 1977-03-21 1977-06-29 Automatic cable equalizer circuit Expired - Lifetime US4151490A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB11903/77A GB1596774A (en) 1977-03-21 1977-03-21 Automatic cable equalizer circuit
GB11903/77 1977-03-21

Publications (1)

Publication Number Publication Date
US4151490A true US4151490A (en) 1979-04-24

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US05/811,291 Expired - Lifetime US4151490A (en) 1977-03-21 1977-06-29 Automatic cable equalizer circuit

Country Status (7)

Country Link
US (1) US4151490A (fr)
JP (1) JPS6056019B2 (fr)
CA (1) CA1083679A (fr)
DE (1) DE2812408C2 (fr)
FR (1) FR2385270A1 (fr)
GB (1) GB1596774A (fr)
NL (1) NL7803010A (fr)

Cited By (35)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4393491A (en) * 1980-11-05 1983-07-12 Anaconda-Ericsson Automatic self-test system for a digital multiplexed telecommunication system
EP0084628A2 (fr) * 1981-12-05 1983-08-03 Robert Bosch Gmbh Montage d'égalisation pour câble
EP0139925A1 (fr) * 1983-09-30 1985-05-08 International Business Machines Corporation Egaliseur automatique d'amplitude
EP0147550B1 (fr) * 1983-11-21 1988-06-22 International Business Machines Corporation Circuits d'égalisation pour canaux d'enregistrement magnétique
US5159275A (en) * 1989-12-06 1992-10-27 Hitachi Denshi Kabushiki Kaisha Method and apparatus for detecting cable length
EP0539173A2 (fr) * 1991-10-25 1993-04-28 Tektronix, Inc. Système de balayage pour télévision par câble utilisant un récepteur commuté
FR2685832A1 (fr) * 1991-12-31 1993-07-02 Thomson Broadcast Systeme correcteur de lignes de transmission.
US5245291A (en) * 1989-12-06 1993-09-14 Hitachi Denshi Kabushiki Kaisha Method and apparatus for detecting cable length
EP0578573A1 (fr) * 1992-07-07 1994-01-12 Alcatel Reseaux D'entreprise Procédé et agencement de correction des pertes affectant un signal vidéo transmis par une liaison de type paires de fils
US5343236A (en) * 1992-06-03 1994-08-30 U.S. Philips Corporation Automatic cable attenuation compensation system
US5455843A (en) * 1992-10-15 1995-10-03 International Business Machines Corporation Adaptive equalizing apparatus and method for token ring transmission systems using unshielded twisted pair cables
US5506549A (en) * 1994-11-14 1996-04-09 Dsc Communications Corporation Cable equalizer
EP0717507A3 (fr) * 1994-12-13 1998-01-21 AT&T Corp. Préaccentuation pour récepteur de modem
US5838726A (en) * 1995-06-29 1998-11-17 Fujitsu Limited Method of automatically adjusting the output voltage in a transmission system
US5953373A (en) * 1995-07-12 1999-09-14 Samsung Electronics Co., Ltd. Equalizing circuit and method for data communication terminal equipment
EP1237294A1 (fr) * 2001-03-02 2002-09-04 Cybex Computer Products Corporation Verfahren und Vorrichtung zur Entzerrung der Kanaleigenschaften in einem Computerverlängerungssystem
US6466626B1 (en) 1999-02-23 2002-10-15 International Business Machines Corporation Driver with in-situ variable compensation for cable attenuation
US6583684B1 (en) * 2000-08-11 2003-06-24 Broadband International, Inc. Method of designing an equalizer and like electronic components
US20040056732A1 (en) * 2000-08-11 2004-03-25 Errington Monte N. Electronic components and method of production
AU781568B2 (en) * 2001-03-06 2005-06-02 Avocent Huntsville Corporation A method and apparatus for equalizing channel characteristics in a computer extension system
US20050134748A1 (en) * 2003-12-17 2005-06-23 David Hoerl Automated system and method for high-frequency signal attenuation compensation
US6940539B1 (en) * 1999-04-30 2005-09-06 General Electric Company Variable cable length compensator for video imaging systems
US20060234546A1 (en) * 2003-07-10 2006-10-19 Masafumi Mori Cable extending device
US20070052849A1 (en) * 2005-09-07 2007-03-08 Intersil Americas Inc. Automatic frequency compensation of video signals transmitted across cables
US20090219980A1 (en) * 2008-02-29 2009-09-03 Analog Devices, Inc. Feedback System and Apparatus for Video Compensation
US7620101B1 (en) 2003-09-24 2009-11-17 Cypress Semiconductor Corporation Equalizer circuit, communication system, and method that is adaptive to varying launch amplitudes for reducing receiver error
US20100110299A1 (en) * 2008-11-03 2010-05-06 Intersil Americas Inc. Systems and methods for cable equalization
US20100110288A1 (en) * 2008-11-03 2010-05-06 Intersil Americas Inc. Cable equalization locking
US20100169559A1 (en) * 1993-09-01 2010-07-01 Eliyahou Harari Removable Mother/Daughter Peripheral Card
US8576966B2 (en) 2010-02-01 2013-11-05 Techwell, Inc. Systems and methods for detecting tampering with video transmission systems
US20130297238A1 (en) * 2012-05-02 2013-11-07 Sony Corporation Detection apparatus, power supply apparatus, power reception apparatus, power supply system, and program
US8872978B2 (en) 2011-06-09 2014-10-28 Intersil Americas LLC Cable equalization and monitoring for degradation and potential tampering
US9160601B2 (en) 2009-01-30 2015-10-13 Intersil Americas LLC Frame structure for a QAM system
CN105407253A (zh) * 2015-11-03 2016-03-16 浙江大华技术股份有限公司 一种确定视频信号衰减数据的方法及装置
US10235315B2 (en) * 2015-04-30 2019-03-19 Fujitsu Limited Communication system, control apparatus, and management apparatus for waveform adjustment based on cable types

Families Citing this family (4)

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Publication number Priority date Publication date Assignee Title
JPS5552645A (en) * 1978-10-14 1980-04-17 Nec Corp Automatic equalizer
DE3248216A1 (de) * 1982-12-27 1984-06-28 Robert Bosch Gmbh, 7000 Stuttgart Verfahren und schaltung zur automatischen einstellung der kabelentzerrung
US4724404A (en) * 1985-11-01 1988-02-09 Hughes Aircraft Company Amplitude-weighting adaptive laser
JPS62135118U (fr) * 1986-02-19 1987-08-25

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DE1259933B (de) * 1962-06-20 1968-02-01 Fernseh Gmbh Schaltungsanordnung zur Entzerrung des Frequenzganges bei der UEbertragung von Videosignalen ueber ein Kabel
US3336540A (en) * 1965-04-15 1967-08-15 Giannini Scient Corp Two channel variable cable equalizer having passive amplitude equalization means in only one of the channels
FR2168188B1 (fr) * 1972-01-19 1974-07-26 Cit Alcatel
US3772617A (en) * 1972-11-02 1973-11-13 Bell Telephone Labor Inc Method and arrangement for setting the remanent flux density in magnetic circuits and equalizer utilizing same
NL7609605A (nl) * 1976-08-30 1978-03-02 Philips Nv Overdrachtsinrichting met een instelbaar net- werk.

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US3079461A (en) * 1951-01-03 1963-02-26 Rca Corp Automatic chroma control
US2798900A (en) * 1951-02-02 1957-07-09 Philco Corp Gain control system for color television receiver

Cited By (52)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4393491A (en) * 1980-11-05 1983-07-12 Anaconda-Ericsson Automatic self-test system for a digital multiplexed telecommunication system
EP0084628A2 (fr) * 1981-12-05 1983-08-03 Robert Bosch Gmbh Montage d'égalisation pour câble
EP0084628A3 (en) * 1981-12-05 1984-12-19 Robert Bosch Gmbh Cable equalizing circuit
EP0139925A1 (fr) * 1983-09-30 1985-05-08 International Business Machines Corporation Egaliseur automatique d'amplitude
EP0147550B1 (fr) * 1983-11-21 1988-06-22 International Business Machines Corporation Circuits d'égalisation pour canaux d'enregistrement magnétique
US5245291A (en) * 1989-12-06 1993-09-14 Hitachi Denshi Kabushiki Kaisha Method and apparatus for detecting cable length
US5159275A (en) * 1989-12-06 1992-10-27 Hitachi Denshi Kabushiki Kaisha Method and apparatus for detecting cable length
EP0539173A2 (fr) * 1991-10-25 1993-04-28 Tektronix, Inc. Système de balayage pour télévision par câble utilisant un récepteur commuté
EP0539173A3 (en) * 1991-10-25 1993-08-11 Tektronix, Inc. Catv sweep system using a gated receiver
EP0550316A1 (fr) * 1991-12-31 1993-07-07 Thomson Broadcast Système correcteur de lignes de transmission
FR2685832A1 (fr) * 1991-12-31 1993-07-02 Thomson Broadcast Systeme correcteur de lignes de transmission.
US5442328A (en) * 1991-12-31 1995-08-15 Thomson Broadcast Transmission line correction system
US5343236A (en) * 1992-06-03 1994-08-30 U.S. Philips Corporation Automatic cable attenuation compensation system
FR2693609A1 (fr) * 1992-07-07 1994-01-14 Alcatel Reseaux Entreprise Procédé de correction des pertes affectant un signal vidéo transmis par une liaison de type paire de fils et interface dotée d'un agencement de correction correspondant.
EP0578573A1 (fr) * 1992-07-07 1994-01-12 Alcatel Reseaux D'entreprise Procédé et agencement de correction des pertes affectant un signal vidéo transmis par une liaison de type paires de fils
US5455843A (en) * 1992-10-15 1995-10-03 International Business Machines Corporation Adaptive equalizing apparatus and method for token ring transmission systems using unshielded twisted pair cables
US20100205360A1 (en) * 1993-09-01 2010-08-12 Eliyahou Harari Removable Mother/Daughter Peripheral Card
US20100169559A1 (en) * 1993-09-01 2010-07-01 Eliyahou Harari Removable Mother/Daughter Peripheral Card
US5506549A (en) * 1994-11-14 1996-04-09 Dsc Communications Corporation Cable equalizer
EP0717507A3 (fr) * 1994-12-13 1998-01-21 AT&T Corp. Préaccentuation pour récepteur de modem
US5838726A (en) * 1995-06-29 1998-11-17 Fujitsu Limited Method of automatically adjusting the output voltage in a transmission system
US5953373A (en) * 1995-07-12 1999-09-14 Samsung Electronics Co., Ltd. Equalizing circuit and method for data communication terminal equipment
US6466626B1 (en) 1999-02-23 2002-10-15 International Business Machines Corporation Driver with in-situ variable compensation for cable attenuation
US6940539B1 (en) * 1999-04-30 2005-09-06 General Electric Company Variable cable length compensator for video imaging systems
US6927645B2 (en) 2000-08-11 2005-08-09 Broadband International, Inc. Electronic component structured to compensate for cable losses and method of production
US20040056732A1 (en) * 2000-08-11 2004-03-25 Errington Monte N. Electronic components and method of production
US6583684B1 (en) * 2000-08-11 2003-06-24 Broadband International, Inc. Method of designing an equalizer and like electronic components
EP1237294A1 (fr) * 2001-03-02 2002-09-04 Cybex Computer Products Corporation Verfahren und Vorrichtung zur Entzerrung der Kanaleigenschaften in einem Computerverlängerungssystem
AU781568B2 (en) * 2001-03-06 2005-06-02 Avocent Huntsville Corporation A method and apparatus for equalizing channel characteristics in a computer extension system
US20060234546A1 (en) * 2003-07-10 2006-10-19 Masafumi Mori Cable extending device
US7440035B2 (en) * 2003-07-10 2008-10-21 Kowa Company, Ltd. Cable extending device
US7620101B1 (en) 2003-09-24 2009-11-17 Cypress Semiconductor Corporation Equalizer circuit, communication system, and method that is adaptive to varying launch amplitudes for reducing receiver error
US20050134748A1 (en) * 2003-12-17 2005-06-23 David Hoerl Automated system and method for high-frequency signal attenuation compensation
US8619024B2 (en) * 2003-12-17 2013-12-31 Riip, Inc. Automated system and method for high-frequency signal attenuation compensation
US20120026401A1 (en) * 2003-12-17 2012-02-02 David Hoerl Automated System and Method for High-Frequency Signal Attenuation Compensation
US8031169B2 (en) * 2003-12-17 2011-10-04 Riip, Inc. Automated system and method for high-frequency signal attenuation compensation
US8341689B2 (en) * 2005-09-07 2012-12-25 Intersil Americas Inc. Automatic frequency compensation of video signals transmitted across cables
US20070052849A1 (en) * 2005-09-07 2007-03-08 Intersil Americas Inc. Automatic frequency compensation of video signals transmitted across cables
US20090219980A1 (en) * 2008-02-29 2009-09-03 Analog Devices, Inc. Feedback System and Apparatus for Video Compensation
US8184723B2 (en) 2008-02-29 2012-05-22 Analog Devices, Inc. Feedback system and apparatus for video compensation
US20100110299A1 (en) * 2008-11-03 2010-05-06 Intersil Americas Inc. Systems and methods for cable equalization
US20100110288A1 (en) * 2008-11-03 2010-05-06 Intersil Americas Inc. Cable equalization locking
US8390740B2 (en) 2008-11-03 2013-03-05 Intersil Americas Inc. Systems and methods for cable equalization
US8451382B1 (en) 2008-11-03 2013-05-28 Intersil Americas Inc. Systems and methods for cable equalization
US8558955B2 (en) 2008-11-03 2013-10-15 Intersil Americas Inc. Cable equalization locking
US9160601B2 (en) 2009-01-30 2015-10-13 Intersil Americas LLC Frame structure for a QAM system
US8576966B2 (en) 2010-02-01 2013-11-05 Techwell, Inc. Systems and methods for detecting tampering with video transmission systems
US8872978B2 (en) 2011-06-09 2014-10-28 Intersil Americas LLC Cable equalization and monitoring for degradation and potential tampering
US20130297238A1 (en) * 2012-05-02 2013-11-07 Sony Corporation Detection apparatus, power supply apparatus, power reception apparatus, power supply system, and program
US9939472B2 (en) * 2012-05-02 2018-04-10 Sony Corporation Detection apparatus, power supply apparatus and power supply system for supplying power
US10235315B2 (en) * 2015-04-30 2019-03-19 Fujitsu Limited Communication system, control apparatus, and management apparatus for waveform adjustment based on cable types
CN105407253A (zh) * 2015-11-03 2016-03-16 浙江大华技术股份有限公司 一种确定视频信号衰减数据的方法及装置

Also Published As

Publication number Publication date
CA1083679A (fr) 1980-08-12
DE2812408C2 (de) 1985-08-08
FR2385270B1 (fr) 1984-06-22
JPS6056019B2 (ja) 1985-12-07
JPS53116719A (en) 1978-10-12
DE2812408A1 (de) 1978-09-28
FR2385270A1 (fr) 1978-10-20
GB1596774A (en) 1981-08-26
NL7803010A (nl) 1978-09-25

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